Low Pressure Underground Steam Pipe Corrosion Protection

Robert10011

Our small co-op in Manhattan has two circa 845 buildings on the lot -- a front building and a smaller carriage house -- separated by a 35 foot deep garden /courtyard.  A Burnham steam boiler is in the front building.  Originally there was a one pipe underground system serving the rear building, but because of water hammer a condensate return tank was installed (with its own return line) around 1985.  That also proved unsatisfactory, and this year we finally determined that both the supply and return lines were pitched in a way that expected water to run uphill. 

So, we dug up the courtyard and just had two new properly pitched lines installed, which seem to work fine without the need for the condensate return tank.  However, before back-filling the trench we are concerned that the pipes are insufficiently protected against corrosion.

The contractor wrapped the pipes with what appears to be ordinary interior appx 4 foot tubes of fiberglass insulation of the type carried by Home Depot.  Held together by some kind of white tape at the joints.   The tubes themselves have  a white exterior with a shiny interior Mylar or aluminum coating.  Inspection noted that the coating of some of the sleeves were pierced by half-**** attempts to support the pipe (without a sand base) with pieces of broken brick.

I bought a roll of shiny Nashua waterproofing repair tape to address the rips, but we are concerned that ordinary interior fiberglass insulation might not do the trick to inhibit exterior corrosion.

We note that Manville makes Zeston (TM) PVC covers for interior steam pipe fiberglass insulating.   Would 4" PVC pipe over our insulated underground supply and return pipes work or would the heat from the supply line melt the protection?

 (Fumes released from heated PVC have been cited as a heath hazard; they definitely caused our Carlisle rubber roof membrane to start falling apart.)

High Density Polyethylene (HDPE) has also been cited as a protective coating over insulation.  Hancor corrugated 4" HDPE drainpipe is sold in 50 and 100 foot rolls by Lowes.  Has anyone thought about using this?   I suppose it's survival depends on the performance of the insulation.

The contractor first mentioned the possibility of coating our pipes with tar, but then backed away from this idea. 

Would appreciate any thoughts about how long the interior fiberglass insulation sleeves will last before deterioration sets in and what we can do now to make the new pipes last longer.

 

 

 

clammy

sch 40 pvc

I have ran wet returns underground using 6 in pvc but i insulated it with 1 1/2 wall insulation and the pvc was placed on a bed of compated quarry dust and 3/4 gravel and buried well below the frost line and i have had no issues ,clammy

Steamhead

Insulation and drainage are key

Insulation to keep the pipes from losing heat, and drainage to keep them dry.



If the pipes get wet from ground water, not only will the insulation lose its effectiveness, but the ground water will boil. You'll have steam in your courtyard.



District-steam companies used to build brick conduits to run their pipes in. You might want to do something similar, along with drain tiles discharging to a storm drain or sump pump. Be sure to include cleanouts in the drain to service it if needed.

Rich Kontny_3

Insul-Pipe

When we did district heating they specified Insul-Pipe with sleeves to slide over the joints. A substance very similar to "Great Stuff" was used to fill the void in the sleeves. These were hot water heating systems, so I do not know if the steam and condensate would be a problem due to high temperatures.



I just checked their website "Insul-pipe " and they do have a steam jacketing system. Give them a shout as the system was easy to work with.



Rich K.

Wayne Heid

FoamGlas

Pittsburgh Corning makes a product called FoamGlas. From your description, it may be just the thing for your application.



http://pcfoamglass.com/solutions_steam.asp



Wayne

TJ_5

pipe insulation

We use a product called DRITHERM  for underground steam condensate lines.  provides both insulation and ground water protection.  comes in bags make form around piping on sides about 6"top/bottom/sides, pour in back-fill.  done.